address PR feedback

* thread safety
* rename a method for clarity

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignalNotifications/OSNotificationsManager.h

@@ -94,7 +94,7 @@ NS_SWIFT_NAME(onClick(event:));
 @property (class, weak, nonatomic, nullable) id<OneSignalNotificationsDelegate> delegate;
 
 + (Class<OSNotifications> _Nonnull)Notifications;
-+ (void)start;
++ (void)startSwizzling;
 + (void)setColdStartFromTapOnNotification:(BOOL)coldStartFromTapOnNotification;
 + (BOOL)getColdStartFromTapOnNotification;
 

iOS_SDK/OneSignalSDK/OneSignalNotifications/OSNotificationsManager.m

@@ -162,13 +162,12 @@ +(void)setDelegate:(id<OneSignalNotificationsDelegate>)delegate {
 static BOOL _disableBadgeClearing = NO;
 
 + (BOOL)isSwizzlingDisabled {
-    static BOOL _cached = NO;
     static BOOL _disabled = NO;
-    if (!_cached) {
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
         id plistValue = [[NSBundle mainBundle] objectForInfoDictionaryKey:ONESIGNAL_DISABLE_SWIZZLING];
         _disabled = plistValue != nil && [plistValue boolValue];
-        _cached = YES;
-    }
+    });
     return _disabled;
 }
 
@@ -245,7 +244,7 @@ + (void)setPushSubscriptionId:(NSString *)pushSubscriptionId {
 
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wundeclared-selector"
-+ (void)start {
++ (void)startSwizzling {
     // Swizzle - UIApplication delegate
     //TODO: do the equivalent in the notificaitons module
     injectSelector(

iOS_SDK/OneSignalSDK/OneSignalNotificationsTests/OneSignalNotificationsTests.swift

@@ -63,7 +63,7 @@ final class OneSignalNotificationsTests: XCTestCase {
 
     func testClearBadgesWhenAppEntersForeground() throws {
         // NotificationManager Start to register lifecycle listener
-        OSNotificationsManager.start()
+        OSNotificationsManager.startSwizzling()
         // Set badge count > 0
         let expectation = self.expectation(description: "Badge set")
         setBadgeCount(1) {
@@ -88,7 +88,7 @@ final class OneSignalNotificationsTests: XCTestCase {
 
     func testDontclearBadgesWhenAppBecomesActive() throws {
         // NotificationManager Start to register lifecycle listener
-        OSNotificationsManager.start()
+        OSNotificationsManager.startSwizzling()
         // Set badge count > 0
         let expectation = self.expectation(description: "Badge set")
         setBadgeCount(1) {
@@ -113,7 +113,7 @@ final class OneSignalNotificationsTests: XCTestCase {
 
     func testUpdateNotificationTypesOnAppEntersForeground() throws {
         // NotificationManager Start to register lifecycle listener
-        OSNotificationsManager.start()
+        OSNotificationsManager.startSwizzling()
 
         OSNotificationsManager.delegate = self
 

iOS_SDK/OneSignalSDK/Source/OneSignal.m

@@ -781,7 +781,7 @@ + (void)load {
         return;
     }
 
-    [OSNotificationsManager start];
+    [OSNotificationsManager startSwizzling];
 
     [[OSMigrationController new] migrate];
 //    sessionLaunchTime = [NSDate date];